In recent years, refractory shotcreting has become an important process for lining, repairing and maintaining refractory linings in steel, non-ferrous metal, chemical, mineral and ceramic processing plants. Shotcreting is usually classified according to the process used, i.e., wet-mix or dry-mix spraying. A dry-mix refractory shotcrete process generally consists of conveying a dry or slightly dampened refractory material through a delivery hose by compressed air to a nozzle where water is introduced to wet the mix prior to application of the refractory material onto a surface. A dry-mix refractory shotcrete process involves transport of the refractory material by large volumes of compressed air. As the result, the velocity of the mix striking the target surface is very high giving good compaction.
A wet-mix refractory shotcrete process generally consists of thoroughly mixing a refractory material and water to produce a pumpable mixture, then introducing the mixture into a delivery hose and pumping the mixture to a dispensing (i.e., spraying) device. A wet-mix process has several advantages over the dry-mix process. For example, a wet-mix process uses materials that do not include clay that may adversely affect the refractoriness of the material. Another is that the refractory materials are more thoroughly mixed with specific amounts of water before the material is conveyed through a dispensing hose to the dispensing nozzle. The thorough mixing of measured amounts of water gives more consistent properties to the refractory mix. A further advantage of a wet-mix process is that less dust is generated during the spraying process. Further, less skill and judgment are required by the nozzle operator compared to a dry-mix process. In this respect, the nozzle operator need only direct the stream as compared to constantly adjusting the water input and directing the stream in a dry-mix process.
Heretofore, because of the inherent weight involved in pumping a wet refractory mix through a delivery hose and the difficulty of maneuvering the same, most delivery hoses are generally 11/2 inch to 2 inches in diameter. In a wet-mix process, air is provided at the nozzle to project the wet-mix refractory onto the surface to be lined. Conventionally, the air lines to the dispensing nozzle are typically 3/8 inch to 1/2 inch. In this respect, compared to a dry-mix process, far less air is used in a wet-mix process. Typically, air is introduced into a standard wet-process nozzle by means of a 3/8 inch or 1/2 inch standard pipe. Air is injected into the refractory in a wet-mix nozzle as a propellant and to break the refractory into a spray (a set modifying admixture is typically introduced into the refractory material at this time). A rubber nozzle tip is used to focus the spray stream of refractory material to establish both a suitable velocity and spray pattern.
The velocity of the refractory material as well as the separation of refractory material within the air stream is based, in part, upon the operating pressure of the air source. Typically, in most factory settings, the air pressure may vary from 60 psi to 100 psi.
Aside from the refractory material used, several factors affect the quality of the applied refractory material. Foremost among the influential factors are the rate of flow of the refractory material into the nozzle, and the airflow to the nozzle to break the refractory into globules of particulate to be sprayed.
The present invention provides an improved method of wet-mix shotcrete spraying, wherein airflow to the dispensing nozzle is increased and an enlarged mixing chamber is provided to break up the refractory material into finer particulate for spraying in a higher velocity stream.